As illustrated by U.S. Pat. Nos. 3,397,428 to Donald, 3,479,425 to Lefevre et al, and 3,860,372 to Newman, Jr., encapsulation of a core stream is known. As exempliifed by Japanese Patent Document No. 55/28825, also known is a multimanifold die in which the center manifold may be partially dammed, to produce a sandwiched core layer, as shown in FIG. 7 thereof.
In the coextrusion art, as exemplified by U.S. Pat. No. 4,197,069 to Cloeren, a melt-laminate may be formed that has a core stream between adjacent streams. In certain cases, it is desirable to isolate the edges of the core stream from flow passageway walls. A deficiency with using encapsulation or sandwiching to provide the isolation, is that the resulting product would include an upper and lower layer of the same composition as the encapsulating or sandwiching material.
Furthermore, it is sometimes necessary as a result of a drawdown effect, to remove edges of an extruded product. When the product includes a special material such as a thermally unstable, corrosive or expensive material, it would be beneficial to isolate the special material from the edges, so that the special material would not be removed during a later trimming step.
A drawback with using an encapsulation or sandwiching process to isolate the special material from the edges, is that, after trimming, the resultant product would include an upper and lower layer of the same composition as the encapsulating or sandwiching material. Accordingly, such an approach lacks flexibility in the selection of an edge material.
Moreover, an extruded product including a core that may be one or more layers, and including a narrow or wide edge layer on one or both sides of the core, is desirable. A problem with using encapsulation or sandwiching to produce this product, is that an upper layer and a lower layer of the same composition as the encapsulating or sandwiching material, would be added to the core, and an edge layer would be added on both sides of the core.
Also known, as illustrated by U.S. Pat. No. 4,533,510 to Nissel, is an edge-laminating apparatus that relies upon an adjustable flow-dividing block in a die manifold. Flow volume per segment into an edge layer channel should be closely matched to the appropriate flow volume per segment in a core channel. Therefore, changing the width of an edge-laminating layer, disadvantageously requires a flow volume adjustment and a mechanical adjustment. Otherwise, flow instability may result, producing a wavy edge-lamination seam. The edge layer channel is parallel to the core channel.
Therefore, there remains a need for an improved edge-laminating apparatus that could isolate the edges of a core stream from flow passageway walls, and that could even isolate a special material such as a thermally unstable, corrosive or expensive material, from the product edges so that the special material would not be removed during a post-extrusion trimming step.
An improved edge-laminating apparatus would provide an even greater contribution to the art, if it could produce an extruded product of varied edge layer width, on one or both sides of a core. Such an apparatus would be especially valuable to the art if it included an easily removable, edge-lamination assembly. The apparatus would be especially useful if it could be included in a feedblock. Such an edge-laminating apparatus would make possible an improved edge-lamination process.